This invention relates to golf clubs and to a method for manufacturing such clubs. The invention is particularly applicable to golf clubs which comprise a head with an associated hosel for connecting the golf club shaft to the head. The invention is further limited to use in connection with heads which have hollow interiors, such heads usually being made of metal or some other non-wood material.
Metal heads have become extremely popular for use in the manufacture of golf clubs, particularly clubs used for longer shots, including the driver and other "woods". These metal club heads typically have at least some hollow portions which keep the heads relatively light-weight. Design techniques, specifically casting techniques, have become sufficiently precise so that such metal heads may be substantially completely hollow although the invention is also applicable to heads which include interior strengthening walls or ribs of some sort.
One problem encountered with a hollow metal head is that a ringing or clanking sound will occur when a ball is struck. In order to overcome this problem, the practice has been to fill the head with a plastic foam so that the sound at impact would be deadened and more like the "solid" sound of a club head made of wood. Thompson Patent No. 4,319,752, Hayashi et al Patent No. 4,451,041, Schmidt Patent No. 4,511,145, Ezaki Patent No. 4,874,171 and Shiotani et al Patent No. 4,988,104 all provide examples of such foam-filled heads.
As set forth, for example in the Ezaki et al disclosure, a rigid urethane foam has been used as a preferred material for filling the interior of a metal golf club head. This foam will achieve the desired results from the standpoint of a sound developed when a ball is struck. It has been found, however, that during use of a club with such rigid foam, there is a tendency for the rigid foam to move relative to the inner walls of the club head. Eventually, this will create a rattling sound, particularly as the relative movement causes a breakdown of the material. This is distracting and also gives the impression of a defective club. Eventually, at least parts of the foam may also turn to powder after continued use so that the sound-deadening function can be lost or at least diminished. The Hayashi patent disclosure teaches the use of pins which penetrate the foam with a view toward positioning and retaining the material and thereby alleviating this problem.